The invention relates to ink jet recording media having high gloss, and in particular to ink jet recording media providing high gloss without calendering or supercalendering.
High quality ink jet recording media are typically made by applying a single layer of coating to a substrate, such as paper or plastic film. The coating is necessarily designed for multi-functionality, e.g., absorption for rapid ink drying, reactivity to hold out ink at the coating surface for maximum print quality, strength for rub-resistance, wet resistance, water fastness, fade-resistance, etc. The coating layer must be applied in an amount sufficient to provide this multi-functionality, and particularly to provide for absorbency of the ink carrier vehicle (usually water) needed for rapid drying time. Typical coat weights are five to eight pounds per functional side per 3300 square feet. Some, but not all, of the functions require expensive coating ingredients.
U.S. Pat. Nos. 4,460,637 and 5,985,424, for example, have suggested that the requisite functionalities might be better or more easily attained by the use of two layers of coating materials having different constituents and different characteristics for serving different purposes. U.S. Pat. No. 5,985,424 in particular proposes use of a first or base coating (which, considering the substrate, may also be referred to as an intermediate layer) designed to have high absorptivity for the ink vehicle and to be compatible in performance with various ink receptive top-coat formulations comprised, in this case, of various ratios of fumed silica and styrene-vinylpyrrolidone. The base coat formulation comprises, by weight, 65-80% precipitated calcium carbonate, 20-30% calcined clay and up to 10% titanium-dioxide, dispersed in a binder comprising 10-15% polyvinyl acetate and 2-5% soy protein.
Calcined clay is significantly different from the clays customarily employed in the coated paper industry, e.g., kaolin clay. Calcined clay has a high surface area and, when applied as a coating and dried, has an open structure providing high void volume. In contrast, conventional clays when dried are comparatively dense with little void volume. Because of its high void volume and large surface area, calcined clay is highly absorbent and would serve well to absorb the ink carrier vehicle. Also, it is much less expensive than other absorbent pigments.
On the other hand, calcined clay is very difficult to work with; it adversely affects coating rheology; and it tends to be abrasive, which can cause rapid wear of converting machinery. Consequently, in the manufacture of ink jet recording media, calcined clay has been relegated to use in minor proportions, if at all.
Whether the substrate is coated with a single layer of coating material or multiple layers of diverse coating materials, if it is desired to have a glossy surface on the recording medium, it is necessary to calender or supercalender either the ink receptive coating or the underlying base sheet. Calendering or supercalendering is necessary to achieve desired gloss or smoothness targets or both. Calendering densifies the medium and leads to a non-porous, and thus non-absorbent, ink-receiving surface. While print quality on these surfaces may be very good, dry times are too long for commercial printing speeds.
The primary object of the invention is to provide a high-quality, high-gloss ink jet recording medium without need for calendering or supercalendering.
Another object of the invention is to provide a high-quality ink jet recording medium having an ink-receiving or receptor coating such that the final print surface has not only the desired gloss and smoothness, but is also porous to enhance drying time.
A further object of the invention is to provide an ink jet recording medium having a high-gloss, porous ink-receiving coating and an absorptive underlying base coating for rapid absorption of excess ink carrier vehicle and rapid drying of the ink.
A still further object of the invention is to provide a high gloss ink jet recording medium having an absorptive intermediate or undercoating comprised of a pigment component and a binder component wherein the pigment component is comprised in major part, more than 50% by weight, of highly absorbent calcined clay.
The high quality, high gloss ink jet recording medium of the invention is comprised of a substrate, such as pre-treated or untreated paper or plastic film, an ink vehicle absorptive coating on the substrate and an ink receptive coating overlying the absorptive coating. The absorptive coating is comprised in major part of a pigment component and in minor part of a binder component, and the pigment component is comprised in major part, i.e., 60-100% and preferably 100%, by weight of calcined clay. The absorptive coating is applied to the substrate at a thickness sufficient to provide a smooth and level surface. The ink receptive or receptor coating is comprised of one or more ink receptive constituents that provide the requisite functionalities of ink hold out, print quality, etc., and that, when applied to the absorptive coating, provide a high gloss print surface without calendering or supercalendering. The ink receiving coating preferably also includes one or more porosity-enhancing constituents to speed up drying time.
The key to the product design is the innovative, intermediate coating between the substrate and the gloss receptor coating. This intermediate coating has the unique ability to provide (1) a very smooth surface for the gloss receptor coating, (2) a base for uniform holdout of the receptor coating, and (3) an absorptive under layer for absorbing excess ink carrier vehicle, e.g., water. Additionally, the intermediate layer or coating imparts dimensional stability to the recording medium for the reason that it prevents moisture changes in either the substrate or the receptor coating from affecting the medium as a whole. Also, the intermediate layer permits use of a porous top coat to achieve outstanding improvements in drying time. And most significantly, it facilitates the production of high quality, high gloss ink jet recording media without requiring calendering or supercalendering.